What about out of the box thinking and using an embedded cellphone. The cell has android grade cpu .5 gb ram 2 gb hard disk, wifi, gsm, gps and of course the full suite of android apps.
Here is one I found on amazon
http://www.amazon.com/Sharp-Unlocked-Touchscreen-Keyboard-Bluetooth/dp/B007V6F2VI/ref=sr_sp-btf_title_1_7?ie=UTF8&qid=1384384147&sr=8-7&keywords=cheap+tablets+under+50+gps

This is the fun part, where the industry is small and everyone is still talking to each other. Soon enough, assuming this industry takes off, we will get to the point where big money is involved and everyone talks through their lawyers and PR departments. It is going to be interesting to see if the open source ethos holds up through this. When IBM published their PC bus specification it was a radical move, and they most likely only got away with doing it because Corporate IBM considered PCs to be inconsequential to "real" computing. This generation is starting out from a different base - I am looking forward to seeing where they end up.